1. Field of the Invention
The present invention relates to a workpiece conveying apparatus for a pressing machine (press machine).
2. Description of the Related Art
As a workpiece (material) conveying apparatus for a transfer press including a plurality of dies for multiple steps (a plurality of steps) aligned along a workpiece conveying direction on one slide or bolster, there has been known a transfer apparatus configured to sequentially convey workpieces through the plurality of dies for the multiple steps (the plurality of steps) from an upstream die to a downstream die.
Hitherto, in the transfer apparatus of this type, transfer working is performed as follows. For example, as illustrated in FIG. 22, two feed bars 10A and 10B extending in the workpiece conveying direction and being arranged opposed to each other approach to, from both sides, workpieces (material) being molded in respective stages (a first stage to a sixth stage are illustrated in FIG. 22) for multiple steps to clamp the workpieces in the respective steps with fingers 20A to 25A and fingers 20B to 25B. In the clamped state, the workpieces are lifted up, advanced (moved to downstream in the workpiece conveying direction), and lifted down. After that, the workpieces are unclamped (the feed bars 10A and 10B are moved apart from each other to release the workpieces) and returned (to original upstream positions in the workpiece conveying direction). Those operations are repeated to convey and work the workpieces through the respective stages.
In the above-mentioned related-art conveying apparatus, in order to achieve operations of the feed bars such as lifting-up-and-down operations, clamping and unclamping operations, and advancing and returning operations, there is often used, for example, a linear-motion mechanism such as a ball screw or a rack and pinion.
Herein, Patent Literature 1 corresponds to Japanese Patent Application Laid-open No. 2011-79004.
Accordingly, in the related-art transfer apparatus, the two feed bars require the plurality of fingers corresponding to the respective stages to hold the workpieces in the respective stages. Consequently, weights of movable components are increased, and there is needed a driving unit capable of exerting a large driving force for simultaneously conveying the workpieces (materials) in all of the stages.
Further, a driving unit for lifting up and down, a driving unit (feed unit) for advancing and returning, and a driving unit for clamping and unclamping are driven by separate servomotors or the like (see FIG. 23A to FIG. 23C). As a result, cost is increased. Further, high-power servomotors are required to move the feed bars (and finger units) having large lengths and large weights at high speed, and the movable components having large weights need to be supported. Thus, strength and rigidity of the apparatus also need to be increased. Consequently, in actuality, cost is increased.
Further, the feed bars (and the finger units) have relatively large lengths and large inertia, and hence higher speed may cause resonance in the feed bars. Thus, in actuality, critical speed is low, and the related-art feed bars are not suitable for high-speed conveyance (see FIG. 23B and FIG. 23C). Further, the movable components have large weights. Thus, in actuality, vibration noise is increased along with an increase in speed.
In recent years, with development of linear motors, similarly to the apparatus described in Japanese Patent Application Laid-open No. 2011-79004, there is an apparatus including the feed bars and the fingers configured to perform the above-mentioned lifting-up, clamping, lifting-down, and unclamping operations by linear motors under a state in which all of the feed bars and the fingers are supported through link mechanisms. However, similarly to the related-art apparatus, the apparatus described in Japanese Patent Application Laid-open No. 2011-79004 has a configuration of advancing and returning all of the feed bars and the fingers. Accordingly, a high-power and large-volume driving unit for advancing and returning is needed. The movable components have large weights, and hence, in actuality, a limitation is imposed on high-speed conveyance.
Further, there is also developed an apparatus of a type in which a linear feeder is interposed between a feed bar and fingers. However, in this type, the above-mentioned advancing and returning operations are merely substituted by an operation of moving the fingers relative to the feed bar in the workpiece conveying direction using a linear motor. In actuality, the related-art driving units as having been provided are used for the lifting-up, lifting-down, clamping, and unclamping operations. The apparatus of this type is actually an apparatus that inevitably requires a high-power servomotor configured to drive large inertia including the feed bar, and is not suitable for high-speed conveyance similarly to the related-art apparatus because of the large inertia.